1. Field of the Invention
The present invention generally relates to nebulizers, and more particularly to the nebulizer with a negative pressure structure.
2. Description of the Related Art
In general, a conventional nebulizer is comprised of a circular piezoelectric plate, a nebulizing plate, a fixing plate and a cavity. For the nebulization of a liquid having a general surface tension, if the total air and liquid pressure value in the cavity is greater than or equal to the external air pressure value (approximately equal to one 1 atmospheric pressure), the pressure at the inner side and the outer side of the nebulizing plate reaches an equilibrium, and a nebulized liquid stored in the cavity can be attached onto an inner side of the nebulizing plate, so that the nebulized liquid will not spill out from the spray hole, so as to achieve the effects of preventing the spray hole from being clogged easily and nebulizing the liquid effectively.
However, for a liquid having a low surface tension, the surface tension cannot be maintained stably due to the too-low surface tension, so that the liquid will not spill from the inner side to the outer side of the spray hole of the nebulizing plate. If the nebulizing liquid has a spilling speed greater than the nebulization speed, the liquid will spill continuously from the spray hole of the nebulizing plate to cover the surface of the nebulizing plate and result in clogging the spray hole and failing to nebulize the liquid effectively.
If the air pressure in the cavity has a positive pressure value, and the nebulized liquid is attached onto the spray hole of the nebulizing plate, and the external air pressure is smaller than the air pressure and liquid pressure in the cavity, then the nebulized liquid in the cavity will spill out from the spray hole of the nebulizing plate to achieve a pressure equilibrium state. As to the liquid with a low viscosity or a general viscosity, the small molecular weight and coherence force between molecules can be separated during the process of passing droplets of the liquid through the spray hole of the nebulizing plate spray hole, so as to achieve an effective nebulization.
However, as to a liquid of a high viscosity, the liquid has a greater molecular weight and Van der Waals' forces between molecules, the adherence force between molecules drives the liquid to spill out from the spray hole of the nebulizing plate, when the molecules of the liquid pass through the spray hole of the nebulizing plate for anebulization. As a result, the spray hole is covered by the liquid and fails to nebulize the liquid effectively. If a negative pressure state can be maintained in the cavity, the nebulized liquid is attached onto the spray hole of the nebulizing plate, and the external air pressure is greater than the pressure in the cavity, then the external air will move from the hole of the nebulizing plate into the cavity for a pressure equilibrium to reduce the spilling and facilitate the nebulized liquid and the external air to be exchanged by vibrations of the nebulizing plate and nebulize the liquid effectively.